Battery packs composed of multiple cells can use internal electronics to assist in managing performance and safety issues. Individual cells can be connected in series to provide higher battery pack voltages for high voltage applications. For some applications, such as electric vehicles or utility-scale energy storage systems, the number of cells connected in series can be in the hundreds or even thousands of cells. Metal hydride cells, such as nickel metal hydride (NiMH), and lithium-based chemistries, such as Li-ion cells, are often used in these battery packs. However, NiMH and lithium-ion cells can be damaged or even explode if undercharged or overcharged. Although internal electronics can be employed to avoid exceeding safe voltages, currents and temperatures within the battery pack, individual cells arranged in a long series can be exposed to variations in local temperature during use, and the performance of individual cells may vary regardless, thereby significantly limiting the capacity of battery packs that employ individual cells in series.
Current methods for balancing a long series of cells often suffer from excessive energy loss during balancing, unreliable operation as a consequence of single-point failures, electronic circuit complexity, inefficient balancing when strings contain hundreds or thousands of cells, and inordinately long times to balance the cells in such strings.
Therefore, a need exists for methods and circuitry for balancing cells that overcome or minimize the above-referenced problems.